Funds are requested to continue studies on the biochemistry and physiology of the mammalian pineal gland, and of the mechanisms that cause daily rhythms in the functional activity of the pineal, the sympathetic nervous system, and other neuroendocrine structures. It is well established that the rodent pineal organ is inhibited by exposing the animal to an environment of light; light is sensed in the retinas, causing nerve impulses to travel along the inferior accessory optic tracts, down the spinal cord, and, via the pre- and post-ganglionic fibers to and from the superior cervical ganglions, to the pineal. The effect of light exposure is to decrease the neuronal input to the pineal; hence less norepinephrine is released by sympathetic nerve terminals, and the activities of the pineal enzymes that make the hormone melatonin (serotonin N-acetyltransferase and hydroxyindole-O- methyltransferase) fall. Although pineal melatonin levels also fall, it has not yet been possible to demonstrate a consequent decrease in melatonin secretion. We hope during the next year to complete development on a method that will allow us to assay melationin levels in human blood and urine, and other body fluids. We have recently found that dopa administration, or the induction of stress (by immobilization or insulin hypoglycemia) elevates pineal melatonin levels in rats; we hope use these inputs to determine whether melatonin secetion also in accelerated. Studies will also continue on mechanisms of photic control of body temperature rhythms, on pineal neuropharmacology, on the effects of melatonin and synthetic congeners on amphibian pigmentation and mammalian neuroendocrine function, and on the biochemical mechanisms by which melatonin modifies brain neurotransmitter metabolism.